In order to improve scratch resistance, optical base materials such as plastic lenses have their surfaces coated with a coating composition which is, then, cured to form a hard coating which is transparent and is highly hard. The coating composition for forming such a hard coating is, usually, blended with fine metal oxide particles, such as a silica sol that is dispersed like a colloid in addition to being blended with an organosilicon compound (curing component for forming film) such as alkoxysilane in order to form a cured body (hard coating) satisfying the above properties and exhibiting excellent adhesion to the base member (see patent documents 1 to 3).
On the other hand, one of the optical base materials that require the above hard coating is a photochromic lens. The photochromic lens is a lens which, when used outdoors where it is irradiated with light containing ultraviolet rays, such as sunlight, quickly develops a color and functions as sunglasses and, when used indoors where it is irradiated with no such light, permits the color to fade out and functions as ordinary transparent spectacles, and its demand is increasing in recent years. An imbibition method, an in-mass method and a coating method have been known for producing photochromic lenses.
The imbibition method is a method of imparting photochromic properties to ordinary plastic lenses by having the surfaces of the plastic lenses without photochromic property imbibe a photochromic compound.
The in-mass method is a method of directly obtaining photochromic lenses by dissolving a photochromic compound in a monomer and polymerizing the monomer in this state.
The coating method is a method of forming a layer (photochromic coating) having photochromic properties by applying a curable composition (photochromic coating agent) containing a photochromic compound onto the surfaces of the plastic lenses and curing the coating.
Among these methods, the coating method, in principle, has an advantage of more easily imparting photochromic properties to any lens base material than the above two other methods. For example, the lens used in the imbibition method must be a soft material which permits the photochromic compound to easily diffuse therein. The in-mass method, on the other hand, must use a special monomer in which the photochromic compound dissolves to a high degree to develop favorable photochromic properties. The coating method, on the other hand, imposes no such limitations on the base member.
Here, when the photochromic plastic lens is produced by the coating method, the photochromic coating formed on the lens base member has a small thickness. To obtain a photochromic coating that develops a color of a practical density, therefore, the coating must contain the photochromic compound at a high concentration. Chromene derivatives are used as the above photochromic compounds. Among them, a chromene derivative having an amino group exhibits particularly excellent coloring property and a quickly fading rate (see patent documents 4 and 5).
A hard coating which is transparent and highly hard is also formed on the surfaces of photochromic lenses produced by the above various methods in order to improve scratch resistance. For example, a patent document 4 discloses an example of using a coating agent (TS56H, trade name) manufactured by Tokuyama Co. being applied on the photochromic coating that contains an amine compound in order to improve close adhesion to the lens base member. This coating agent is a product produced by the present applicant and is a curable composition containing a silica sol and alkoxysilane other than tetraalkoxysilane.                Patent document 1: JP-A-53-111336        Patent document 2: JP-A(T2)-2001-520699        Patent document 3: JP-A(T2)-2002-543235        Patent document 4: leaflet of International Laid-Open WO2003/011967        Patent document 5: JP-A-2003-342310        